The invention concerns a unit for deflating and/or inflating tires, in particular on off-road-capable vehicles, having a regulating device that has an air input connectable to a compressed-air source and an air output that can be connected via air-pressure lines to the tires, the regulating device having a regulating member with which a specific working pressure can be implemented in the air-pressure lines after connection to the tires, the regulating member being connected to a manually actuable adjusting device with which different working pressures can be established.
A unit of this kind is described in DE Utility Model 91 09 984.6. The unit is used, in particular on off-road-capable vehicles, to adapt the tire pressure to particular surface conditions. On paved roads, for example, the tires of such vehicles require a high pressure so that they do not heat up excessively at speeds in the vicinity of the maximum speed, and in order to ensure good road-holding. On unpaved roads and especially off-road, where the vehicle is driven slowly, lower tire pressures are advantageous because traction is thereby improved and the creation of deep tire tracks and severe surface compaction is prevented.
The aforesaid unit has a regulating device that has an air input which is connectable to a compressed-air source. Compressed-air sources of this kind are generally present in any case on large off-road-capable vehicles in order to actuate other devices, for example brakes. The regulating device has an air output that can be connected to a compressed-air line which are connectable, after branching, to the tire valves. The branched compressed-air lines are each stored in receiving containers in the vicinity of the tires, and for the inflation or deflation operation - when the vehicle is stationaryxe2x80x94can be pulled out and connected to the valves.
The regulating device has a regulating member in the form of a proportional valve with which a specific working pressure can be established at the air output when the compressed-air lines are connected to the tire valves. Using a pneumatic adjusting device, various working pressures can be established in order to adapt the tire pressure to different driving surface conditions. For this purpose, the adjusting device has pressure valves that communicate with the compressed-air source and with which a specific control pressure can be applied to the proportional valve. The control pressure possesses a specific relationship to the working pressure, i.e. the working pressure is implemented by the proportional valve in accordance with the control pressure acting on it. The control pressure and thus the working pressure can be adjusted to various values by way of an adjusting member to be actuated from outside. The adjusting member is arranged on the exterior of the housing of the regulating device.
Although the known unit operates reliably, adjusting errors have occurred when the unit is operated. It has been found that despite the operating instructions and labeling on the adjusting member, incorrect tire pressures are often established; on the road, this can result in severe tire wear and even burst tires, and off-road it can produce poor traction and severe surface compaction.
It is therefore the object of the invention to configure a unit of the kind cited initially in such a way that the tire pressure optimal for the particular surface condition is established with greater reliability.
According to the present invention, this object is achieved in that the adjusting device has at least two, preferably three to six manually actuable switching members or a stepped switching member having at least two, preferably three to six switch positions, actuation of which allows the regulating member to be respectively adjusted to a working pressure associated with the switching member. The basic concept of the invention is thus to make available to the operator a separate switching member for each working pressure, so that the operator can establish the respective desired working pressure (and therefore tire pressure) by simply actuating the switching member provided therefor. The consideration underlying both solutions is the fact that generally only a few different working pressures are necessary for adaptation to the various surface conditions. Three different working pressures, and consequently three switching members or three switch positions of the stepped switching member for each working pressure, will normally be sufficient to adapt the tires to the various surface conditions.
Operation has proven to be very much more reliable, since it is now sufficient to briefly actuate one of the adjusting members or the stepped switching member. The switching members can be configured as simple two-point switches, for example as push switches, rotary switches, or rocker switches, while a rotary switch or slide switch is suitable for the stepped switching member. Corresponding labeling and/or colors can be used to ensure that the operator actuates the particular adjusting member, or brings the stepped switching member into that switch position, which brings about a working pressure corresponding to the particular surface conditions.
The stepped switching member can be connected to electropneumatically actuated valves. A particularly simple embodiment results, however, if the stepped switching member is coupled directly to a multiple-way valve.
The switching members or the stepped switching member can be arranged on the regulating device itself. Since the latter is usually arranged in the center of the vehicle in order to ensure short compressed-air lines to the tires, the regulating device is often not readily accessible, and in addition is more greatly subject to environmental influences such as dirt, etc. It has therefore proven advantageous to arrange the switching members or the stepped switching member on an adjusting unit, separated from the regulating device, that is connected to the regulating device via pneumatic or electrical control lines and thus can be mounted at any desired location on the vehicle. The driver""s compartment is especially suitable for this purpose, since there the adjusting unit can be operated in convenient and well-protected fashion. Several identical and separate sets of switching members or several stepped switching members can, of course, also be present concurrently.
In a further embodiment of the invention, provision is made for an adjusting element to be present with which a working pressure of zero can be established. This is a further switching member that can be configured as an on/off switch. In the OFF position, the regulating member automatically vents the compressed-air lines so that rapid deflation of the tires can be performed, so as to transition in the shortest possible time, for example, from the high pressure for road operation to the substantially lower pressure for off-road use. The pressure is then set precisely to the predefined value by activating the adjusting element and actuating the switching member provided for off-road use, or setting the relevant switch position on the stepped switching member.
According to a further feature of the invention, provision is made for the regulating member to be pneumatically adjustable, for the adjusting device to have a pneumatic circuit in which each switching member or each switch position has associated with it a pneumatic pressure regulating valve for regulating a specific control pressure for the regulating member, and for the pressure regulating valves to be connected to an air-pressure reservoir. Suitable pressure regulating valves include precision valves with which the respective control pressure and thus also the working pressure at the output of the regulating device can be established very accurately. In order for the pressure of the air-pressure reservoir to be as constant as possible it should be protected with respect to the air-pressure source by way of a nonreturn valve. It is advantageous to associate a switching valve with each pressure regulating valve, and to connect the switching valves to the switching members or to the stepped switching member.
The regulating valve is advantageously configured in the regulating unit as a proportional valve. A separate pressure reservoir should be associated with it. Lastly, the invention provides for the working pressures associated with the switching members to be adjustable. This should be possible, however, only in such a way that the operator cannot easily make the adjustment. The adjustment should be performed only in a repair shop by a person authorized to do so, so that incorrect settings do not occur when changing pressures to adapt to different surface situations.